Rowing is a cyclic (or intermittent) form of propulsion such that in the quasi-steady state the motion of the system (the system comprising the rower, the oars, and the boat), is repeated regularly. In order to maintain the steady-state propulsion of the system without either accelerating or decelerating the system, the sum of all the external forces on the system, averaged over the cycle, must be zero. Thus, the average drag (retarding) force on the system must equal the average propulsion force on the system. The drag forces consist of aerodynamic drag on the superstructure of the system (components of the boat situated above the waterline), as well as the hydrodynamic drag on the submerged portion of the system. The propulsion forces are the forward reaction of the water on the oars while in the water. Note also that the oar can be used to provide a drag force (a force acting against the forward motion) when the system is brought to rest.
There are 4 main rowing machine types that are classed according to its utilized resistance mechanism. Having an exercise workout needs to have resistance against the movement in order to provide to the muscles and the cardiovascular system a good change. This can be provided by the rowing machine whenever you pull its handle and then slide back to the seat. Having low resistance works on the cardiovascular system can make you row fast easily. Having high resistance means that it provides you with the anaerobic session, working with the muscles harder, also having a slow stroke rate because of the harder pull.
If you're looking at a WaterRower, you're probably also considering the Concept2. They're both great machines, but which you choose depends on your needs. I think the WaterRower is ideal for most people, but not everyone. The WaterRower has a number of advantages vs the Concept 2 - it is quieter, the mechanism up front is lower profile, it has a comfortable seat, it is much better looking, it's easier to stand up when you're not rowing and it's just ... zen-like. There is something about the smoothness of the WaterRower that makes it a joy to use, and because it's quiet you can easily stream your favorite binge-series without cranking the volume too high.
This affordable rowing machine is streamlined, simple to use, built well, has a comfy seat with a realistic rowing movement, and especially good for a newbie. Because the cost of this machine is less than $150, it is popular on the net. As it has a hydraulic rower, resistance is provided by just one piston under the main key column. Along with a comfy cushioned seat, LCD screen, this machine provides 12 hydraulic cylinder resistances.